msm: mdss: Allow smp change during composition switch

The composition fallback mechanism might not ensure unsetting of
the pipe whose prepare call failed due to smp configuration change,
typically in the cases where change in composition requests same
pipe. This scenario is a deadlock where composition switch does
not happen, due to these pipe failures.

To handle such cases, for changed SMP request for a pipe doing
non backend composition, allow smp configuration to happen, so
that the composition could be successfully switched, thereby
preventing the deadlock.

Change-Id: I2d29ac6591671494abc7c4caf7c6c53f058d12f6
Signed-off-by: Justin Philip <jphili@codeaurora.org>